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Proceedings Paper

Initial Operation Of A Polarization-Controlled Beamed Ech Launcher
Author(s): T. S. Bigelow; C. R. Schaich; T. L. White
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Paper Abstract

A system for launching 53.2-GHz electron cyclotron heating (ECH) power is being installed on the Advanced Toroidal Facility (ATF) fusion experiment at Oak Ridge National Laboratory. The launcher provides a narrow linearly polarized beam. The plane of polarization is easily rotated. Measurements indicate that the launcher will have a -20 dB beam width of 15 cm at the plasma center and polarization purity of >97%. The ATF (1) requires 53.2-GHz microwave power for ECH plasma ionization and heating; this power is generated by a 200-kW cw gyrotron. Theoretical ray tracing studies have shown almost complete first-pass power absorption is possible if the power is within the saddle point in the proper polarization (2). Therefore, a narrow-beam-width launcher with adjustable polarization is being developed. In ATF the confining magnetic field can operate continuously at 1 T or in long pulses at 2 T. Either second harmonic or fundamental ECH absorption occurs, depending on the field strength, and it is of interest to operate experiments using both values. With perpendicular propagation and low-field-side launch, the ECH power must be in the extraordinary mode (X-mode, Erf perpendicular to Bo) for second harmonic (co = 2 wee) or in the ordinary mode (0-mode, Enr parallel to Bo) for fundamental (o) = c),) operation. The magnetic field in ATF is formed primarily by helical windings, which produce a shear in the plane of the field along a radial chord. This shear may cause polarization rotation of the ECH wave as it travels through the outer plasma regions because of the unequal 0- and X-mode phase velocities at higher plasma density (similar to Faraday rotation). The ECH resonance zone is a 10-cm-wide saddle point near the plasma center.

Paper Details

Date Published: 18 November 1989
PDF: 2 pages
Proc. SPIE 1039, 13th Intl Conf on Infrared and Millimeter Waves, (18 November 1989); doi: 10.1117/12.978359
Show Author Affiliations
T. S. Bigelow, Oak Ridge National Laboratory (United States)
C. R. Schaich, Oak Ridge National Laboratory (United States)
T. L. White, Oak Ridge National Laboratory (United States)

Published in SPIE Proceedings Vol. 1039:
13th Intl Conf on Infrared and Millimeter Waves
Richard J. Temkin, Editor(s)

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